Semicoductor component and a method for producing the same

ABSTRACT

The present invention relates in particular to a semiconductor component, such as especially a humidity sensor ( 200, 300, 400, 500, 600, 700, 800 ), which has a semiconductor substrate ( 101 ), like in particular of silicon, a first electrode ( 102 ) and a second electrode ( 202 ) and at least one first layer ( 101 ) that is accessible for a medium acting from the outside on the semiconductor component, the first layer being arranged at least partially between the first and the second electrode.  
     Particularly to reduce the costs for producing the semiconductor component, according to the present invention, the first layer has pores ( 301 ) into which the medium reaches at least partially.

BACKGROUND INFORMATION

[0001] The present invention is based on a semiconductor component like,in particular, a humidity sensor, and a method for producing asemiconductor component according to the definition of the species inthe respective independent patent claim.

[0002] Known multi-layer semiconductor components for ascertaining thequantity and/or the type of a medium acting on the semiconductorcomponent have a capacitor arrangement. The medium acts on a layerlocated between a first and a second electrode. In the case of asemiconductor component which forms a humidity sensor, this is thehumidity in the air surrounding the semiconductor component. In a knownhumidity sensor, atmospheric humidity penetrates through a patterned topelectrode into the moisture-sensitive layer and changes the dielectricconstant of this layer. This leads to a moisture-dependent change in thecapacitance of the capacitor formed by the two electrodes and themoisture-sensitive layer, which is evaluated.

SUMMARY OF THE INVENTION

[0003] In contrast, the semiconductor component of the present inventionhaving the characterizing features of the respective independent patentclaim has, in particular, the advantage that it has a layer which isprovided with pores and may be produced inexpensively. The medium to bedetermined qualitatively and/or quantitatively gets into it, therebychanging the dielectric constant of the porous layer. Such a layer ispreferably a silicon layer that is porous or is provided with pores. Incontrast to a known capacitive humidity sensor provided with a polymerlayer, the porous layer of the present invention exhibits nomoisture-dependent swelling.

[0004] With the semiconductor component of the present invention, usingsuch a porous layer, a sensor may be inexpensively produced both for agaseous and for a liquid medium, which, in addition, is characterized bygreat durability and reliability. The semiconductor component ispreferably built as a sensor for determining the atmospheric humidity.

[0005] A method of the present invention proposes producing the at leastone porous layer of the semiconductor component according to theinvention using one or more etching media containing hydrofluoric acid.Preferably, the porosity in the starting layer of the semiconductorcomponent of the present invention for producing the porous layer isproduced by applying an electric field between the upper side and thelower side of the semiconductor component, and an accompanying flow ofelectric current through the etching medium or the etching media. Theporosity, i.e. particularly the relationship of the total extent of thehollow space of all pores to the volume of the remaining material of thelayer may be adjusted in a simple, reproducible manner by applying asuitable electric voltage. In particular, the etching process may bestopped largely abruptly with the switch-off of the voltage. Theproduction process may thereby be controlled well.

[0006] According to one preferred specific embodiment of the invention,the etching medium and/or the etching media for producing the pores ishydrofluoric acid (HF) or a liquid mixture or a chemical compound whichcontains hydrofluoric acid.

[0007] In one preferred embodiment of the invention, a highly volatilecomponent, preferably an alcohol such as ethanol, and/or purified wateris added to the etching medium(s) to dilute it/them.

[0008] Ethanol reduces the surface tension of an etching medium providedwith it, thereby permitting better wetting of the silicon surface and abetter penetration of the etching medium into etched pores. Moreover,the bubbles developing during the etching process are smaller thanwithout the addition of ethanol to the etching medium, and the bubblesare thus able to escape better through the pores already formed.

[0009] According to one preferred specific embodiment of the invention,the etching medium, the HF-concentration in the etching medium and/orthe doping of the region to be etched and/or the temperature andpossibly other process parameters of the etching method is/are selectedin such a way that the etching process, i.e. the pore formation, may beadjusted in a suitable manner and/or may be stopped, preferably largelyabruptly, with the switch-off of the electric voltage.

BRIEF DESCRIPTION OF THE DRAWING

[0010] The semiconductor element of the present invention and itsmanufacturing method are described in detail in the following utilizingschematic drawings which are not necessarily true to scale, using ahumidity sensor as an example, the same reference numerals designatingthe same or equally-acting layers or parts. The Figures show:

[0011]FIG. 1 a known humidity sensor having a bottom electrode, apatterned top electrode and an overetched polymer layer located betweenboth electrodes—in cross-section;

[0012]FIG. 2 the preliminary stage of a first specific embodiment of ahumidity sensor according to the present invention—in cross-section;

[0013]FIG. 3 a first further development of the first specificembodiment shown in FIG. 2—in cross-section;

[0014]FIG. 4 a second further development of the first specificembodiment shown in FIG. 2—in cross-section;

[0015]FIG. 5 an exemplary embodiment of a humidity sensor from FIGS. 3or 4, provided with electrical connections—in cross-section and in planview;

[0016]FIG. 6 a first variant of a second specific embodiment of ahumidity sensor according to the present invention, having twoelectrodes arranged at the same level and a screening electrode locatedabove them—in cross-section;

[0017]FIG. 7 the humidity sensor of the present invention shown in FIG.6 without screening electrode—in cross-section;

[0018]FIG. 8 the humidity sensor of the present invention shown in FIG.6 without screening electrode and without intermediate layer—incross-section;

[0019]FIG. 9 a first specific embodiment for the bottom electrodes,shown in FIGS. 6 through 8, in the form of a plate-type capacitor—inplan view;

[0020]FIG. 10 a second specific embodiment for the bottom electrodes,shown in FIGS. 6 through 8, in the form of an interdigital structureformed by two intermeshing comb-type electrodes—in plan view; and

[0021]FIG. 11 another humidity sensor according to the present inventionwhich has a reticular upper electrode and a reticular lower electrode—incross-section.

[0022] Known humidity sensor 100, shown in FIG. 1, has a siliconsubstrate 101, a bottom electrode or lower electrode 102 formed by asuitably doped region in silicon substrate 101, an overetched polymerlayer 103 and a patterned top electrode 104. Air reaches polymer layer103 via the patterning or openings in patterned top electrode 104. Themoisture contained in the air reaches polymer layer 102 and influencesits dielectric constant. The dielectric constant of polymer layer 103may be determined via lower electrode 102, polymer layer 103 andpatterned top electrode 104 which form a plate-type capacitor. Theinstantaneous atmospheric humidity is ascertained on the basis of thedielectric constant.

[0023] Changing atmospheric humidity disadvantageously leads toshrinking or swelling of the polymer layer, which after some time mayresult in mechanical destruction of known humidity sensor 100. Inaddition, the construction of the known humidity sensor using a polymerrequires considerable outlay and is therefore costly for a mass-producedproduct, particularly in the automobile sector.

[0024] Preliminary stage 200 of a first specific embodiment of ahumidity sensor according to the present invention shown in FIG. 2 has asilicon substrate 101, a bottom electrode or lower electrode 102 formedby a doped region, a so-called intermediate layer 201 made of silicondeposited on the upper side of silicon substrate 101 and doped region102, a top electrode or upper electrode 202 formed by a doped region,and a masking, formed by a mask layer 203, of the upper side ofintermediate layer 201. The masking of the upper side of intermediatelayer 201 is such that an etch opening 204 is formed above lowerelectrode 102, intermediate layer 201 and upper electrode 202.Preliminary stage 200 has been produced by known silicon semiconductorprocesses, so that it is not necessary to discuss it in greater detailhere.

[0025] To produce a perforated or porous top electrode 202 as well as aperforated or porous intermediate layer 201, in each case preferablyrestricted to the region below etch opening 204, preliminary stage 200shown in FIG. 2 is preferably put into an etching medium that, inparticular, contains hydrofluoric acid. An electric voltage is appliedbetween the upper side of preliminary stage 200 and the lower side ofpreliminary stage 200. The electric voltage causes current to flow inthe etching medium which produces pores or openings in top electrode 202and subsequently in intermediate layer 201, in each case largelyrestricted to the region below etch opening 204. The result of theelectrochemical etching using hydrofluoric acid is first furtherdevelopment 300, shown in FIG. 3, of the first specific embodiment shownin FIG. 2. The process parameters have been set during the etching insuch a way that the porosity of the relevant region of top electrode 202and of relevant region 301 of intermediate layer 201 are substantiallyidentical. To be understood by porosity is, in particular, therelationship of cavity space or space accessible from the outside, whichis given by the pores formed in the relevant regions, to the volume ofthe remaining material of the layer specific to a volumetric unit.

[0026] Production of a top electrode 202 whose porosity is substantiallythe same as the porosity of intermediate layer 201, located below andnext to it, in relevant regions 301, is preferably achieved according tothe present invention in that the intensity of the current flowingthrough the etching medium when producing the pores in top electrode 202and subsequently when producing the pores in intermediate layer 201situated below it is largely identical. If necessary, when adjusting thecurrent intensity for producing the porosity in top electrode 202, itmust be taken into account that region 202 is doped differently fromintermediate layer 201. Given etching parameters which are otherwiseconstant, the depth of the porous etching is preferably predetermined bythe period of time during which the electric current flows through theetching medium.

[0027] The humidity sensor of the present invention shown in FIG. 3forms a capacitor having a porous, thin, upper electrode 202 and aporous region 301 in intermediate layer 201 between upper electrode 202and lower electrode 102. Porous region 301 of intermediate layer 201supports upper electrode 202. Humid air is able to get into porousregion 301 of intermediate layer 201 through the fine pores of thin,upper electrode 202, relative to the thickness of intermediate layer201. Therefore, the dielectric constant, and thus the evaluablecapacitance between the upper and lower electrodes changes as a functionof the specific atmospheric humidity.

[0028] The controlled utilization of the dependence of the form of theporosity on the doping is also possible. For example, by using ann-doping for the upper electrode, one would obtain vertical pores, andby using a p-doping for the intermediate layer, one would obtain finelybranched pores.

[0029] As will be explained in greater detail later in connection withFIG. 5, the two electrodes may be electrically connected via dopedregions in the form of printed circuit traces to contact pads or contactareas, or to a circuit (not shown) integrated on the sensor. Inaddition, it is also possible to produce on the sensor a referencecapacitor that, for example, is covered over the entire surface withmetal during the subsequent metallization step. Alternatively, thecovering may also be implemented by a passivation applied separately. Inthis manner, the reference capacitor is no longer sensitive to moisture.

[0030]FIG. 4 shows a second further development of the preliminary stageof a first specific embodiment shown in FIG. 2. In contrast to the firstfurther development, shown in FIG. 3, of the preliminary stage of afirst specific embodiment shown in FIG. 2, in region 401 of upperelectrode 202 or of upper intermediate layer 201, the humidity sensor ofthe present invention shown in FIG. 4 has a porosity which isperceptibly less than the porosity of intermediate layer 201 locatedbelow upper electrode 202. To achieve this, upper electrode 202, i.e.the corresponding doped region which forms the upper electrode, isporously etched in a time-controlled manner by applying an electricvoltage in hydrofluoric acid. In so doing, work is carried out using alow current density. This causes a low porosity. After intermediatelayer 201 has been porously etched in the region of upper electrode 202,the current density is markedly increased. The underlying intermediatelayer is now likewise porously etched, but with a perceptibly higherporosity compared to the porosity of upper electrode 202. The porouslyetched regions are delimited laterally by mask layer 203. In contrast tothe first further development, intermediate layer 201 is markedly moreporous than the doped region or the doped layer which forms upperelectrode 202, as already explained. The advantage in this preferredspecific embodiment of the invention is that the change in thedielectric constant in response to a change in the atmospheric humidity,which acts on the humidity sensor of the present invention, happensprimarily—as desired—in intermediate layer 201 or in the interveningspace between the upper and lower electrodes. Care must be taken in theporous etching of the present invention that the porous residualmaterial in the intervening space between the upper and lower electrodesis still stable enough that it provides sufficient mechanical supportfor the upper electrode.

[0031]FIG. 5 shows, in cross-section and in plan view, the exemplaryembodiment of a humidity sensor 500 from FIGS. 3 or 4, provided withelectrical connections. Lower electrode 102 is connected via a suitable,known plated-through hole 501 to a contact area 502 for its externalcontacting. Upper electrode 202 is connected via a suitable, knowncontact deck 504 to a contact area 503 for its external contacting. Thecapacitance of the capacitor formed by upper electrode 202, lowerelectrode 102 and porous layer 301 or 402 located in between isdetermined via the external contactings. As already explained, thedielectric constant of the porous layer situated between the twoelectrodes is a function of the specific medium which is able topenetrate from the outside into the pores of the porous layer. In thesame way, the dielectric constant of the porous layer is a function ofthe concentration of the medium in question. In the example of ahumidity sensor described here, atmospheric humidity penetrates viaporous upper electrode 202 into porous region 301 or 402, so that thecapacitance of the capacitor changes. This change is supplied viacontact areas 502 and 503 to an evaluation circuit (not shown) whichascertains or quantitatively determines the capacitance change and thechanged atmospheric humidity giving rise to it. To this end, a referencecapacitor may be used, for example, which is likewise integrated on thesemiconductor component (not shown).

[0032] While the upper part of FIG. 5 shows humidity sensor 500 incross-section, the lower part of FIG. 5 shows humidity sensor 500 inplan view. It may be inferred from the plan view of humidity sensor 500that lower electrode 102 and upper electrode 202 have a rectangularoutline, and are arranged in parallel, displaced in height relative toeach other. Their outlines largely coincide.

[0033] First variant 600 of a second specific embodiment of a humiditysensor according to the present invention shown in FIG. 6 has twoelectrodes 601 and 602 arranged at the same level. It is inferable fromthe cross-section of the first variant, i.e. from semiconductorcomponent 600 shown in FIG. 6 that first electrode 601 and secondelectrode 602 are covered by a screening electrode 603. Screeningelectrode 603, the region of intermediate layer 201 below screeningelectrode 603 and the region between first electrode 601 and secondelectrode 602 have been made porous in the manner described. In theexample of a humidity sensor presented here, atmospheric humidity getsbetween first electrode 601 and second electrode 602 via the pores inscreening electrode 603, the porous region (not shown) of intermediatelayer 201 and the porous region (not shown) between electrodes 601 and602. The dielectric constant of the porous region between firstelectrode 601 and second electrode 602 thereby changes, which means thecapacitance of the described capacitor changes. The change incapacitance is evaluated in known manner for the quantitativedetermination of the atmospheric humidity.

[0034]FIG. 7 shows the humidity sensor of the present invention depictedin FIG. 6 without screening electrode 603. Like the exemplary embodimentshown in FIG. 6, the specific embodiment of a semiconductor component700 shown in FIG. 7 has an intermediate layer 201 that has been madeporous by the aforesaid measures in the region of first electrode 601and second electrode 602. In the same way, the region between firstelectrode 601 and second electrode 602 of specific embodiment 700 inFIG. 7 is porous, so that atmospheric humidity acting from outside onsemiconductor component 700 leads to a change in the dielectric constantof the layer between the two electrodes 601 and 602, which is evaluatedin the manner described for the quantitative ascertainment of theatmospheric humidity.

[0035] Humidity sensor 800 shown in FIG. 8 differs from the specificembodiment shown in FIG. 6, in that it has neither a screening electrode603 (see FIG. 6) nor a porous intermediate layer 201 (see FIG. 7). Thus,humidity sensor 800 shown in FIG. 8 has only a silicon substrate 101 andtwo suitably doped regions which form first electrode 601 and secondelectrode 602. Humidity sensor 800 again has a porous region or a porouslayer (not explicitly shown) between the two electrodes 601 and 602. Inthe same way as for the semiconductor component shown in FIG. 6 and FIG.7, atmospheric humidity acting on humidity sensor 800 from the outsidegets between the two electrodes 601 and 602 and changes the dielectricconstant of the porous layer situated between the two electrodes. Theaccompanying change in capacitance is again detected in the known mannerfor ascertaining the atmospheric humidity currently acting on thehumidity sensor.

[0036]FIG. 9 shows a first specific embodiment 900 for the electrodes,shown in cross-section in FIGS. 6 through 8, which form a plate-typecapacitor. Plate-type capacitor 900 has a first bottom electrode 901 anda second bottom electrode 902.

[0037]FIG. 10 shows a second specific embodiment for the electrodesshown in cross-section in FIGS. 6 through 8. They have the form of twointermeshing comb-type electrodes 1001 and 1002 which form a so-calledinterdigital structure 1000.

[0038]FIG. 11 shows another humidity sensor 1100 according to thepresent invention—in cross-section. Silicon substrate 1101 and siliconintermediate layer 1102 of FIG. 11 have a suitable p-doping. On p-dopedsilicon substrate 1101, a—in plan view (not shown)—reticular or latticedlower electrode, which is designated by 1103 in the cross-sectionaldrawing, has been formed by an n-doped region, corresponding to thisform, in silicon substrate 1101.

[0039] P-doped silicon intermediate layer 1102 has been deposited onsilicon substrate 1101 and the n-doped region, i.e. lower electrode1103. Silicon intermediate layer 1102 is likewise provided with ann-doping in such a way that, in turn, an n-doped region is formed. Then-doped region in turn forms a—in plan view (not shown)—reticular orlatticed upper electrode designated in the cross-sectional drawing ofFIG. 11 by 1104. The production of the n-doped regions and thedeposition of the intermediate layer are carried out in known manner, sothat it is not necessary to discuss it in greater detail.

[0040] To produce porous region 301 of FIG. 11, the structure of FIG. 11described above is etched electrochemically in the manner alreadydescribed. Because of the voltage difference between the upper side andthe lower side of the structure shown in FIG. 11, during the etchingprocess, an electric current flows which, starting from the etchingmedium surrounding the structure of FIG. 11, flows substantiallyuniformly through p-doped, epitactically deposited intermediate layer1102, and flows past the n-doped electrodes without penetrating them.Expressed differently, the current density in the n-doped electrodes islargely negligible compared to the current density in intermediate layer1102. The result is that, during the etching process, pores are formedalmost exclusively in layer 1102 and not in latticed electrodes 1103 and1104. That is to say, only intermediate layer 1102 is porous below etchopening 204 in the etch mask; in contrast, electrodes 1103 and 1104 arenot, or are largely not porous. Porous region 301 in intermediate layer1102 is then used in the manner already described for the quantitativeand/or qualitative determination of the medium like, in particular, airwhich has penetrated from above into the intermediate layer. Themoisture or water content of the air may be determined capacitively withthe aid of the structure, shown in FIG. 11, which, in particular, isintended to form a humidity sensor according to the present invention.N-doped electrodes 1103 and 1104 of the present invention arecharacterized in that they are not affected during the electrochemicaletching. Therefore, their electric conductivity is largely retained inspite of the etching process (no material removal). In addition, leakagecurrents may be substantially avoided by the use of n-doped electrodesin p-doped material such as, in particular, silicon.

[0041] List of Reference Numerals

[0042]100 known humidity sensor

[0043]101 silicon substrate

[0044]102 bottom electrode, lower electrode, formed by suitably dopedregion

[0045]103 overetched polymer layer

[0046]104 patterned top electrode, upper electrode

[0047]200 preliminary stage of a first specific embodiment of a humiditysensor according to the present invention

[0048]201 silicon intermediate layer

[0049]202 top electrode, upper electrode, doped region

[0050]203 mask layer

[0051]204 etch opening

[0052]300 first variant of the first specific embodiment shown in FIG. 2

[0053]301 porous region in intermediate layer 201, which extends in theentire region below etch opening 204 up to bottom electrode 102

[0054]400 second variant of the first specific embodiment shown in FIG.2

[0055]401 region having low porosity, which extends in the region belowetch opening 204 up to approximately the lower side of top electrode 202

[0056]402 region having great porosity, in relation to region 401, whichextends in the region below etch opening 204 up to approximately thelower side of bottom electrode 102

[0057]500 exemplary embodiment of a humidity sensor from FIG. 3 or 4,provided with electrical connections, in cross-section and in plan view

[0058]501 plated-through hole

[0059]502 contact area for contacting of the bottom electrode

[0060]503 contact area for contacting of the top electrode

[0061]504 contact deck for contacting of the top electrode

[0062]600 first variant of a second specific embodiment of a humiditysensor according to the present invention, having two electrodesarranged at the same level and a screening electrode located above them

[0063]601 first bottom electrode

[0064]602 second bottom electrode

[0065]603 screening electrode

[0066]700 the humidity sensor of the present invention shown in FIG. 6without screening electrode

[0067]800 the humidity sensor of the present invention shown in FIG. 6without screening electrode and without intermediate layer

[0068]900 a first specific embodiment for the electrodes, shown in FIGS.6 through 8, in the form of a plate-type capacitor

[0069]901 first bottom electrode

[0070]902 second bottom electrode

[0071]1000 a second specific embodiment for the electrodes, shown inFIGS. 6 through 8, in the form of an interdigital structure formed bytwo intermeshing comb-type electrodes

[0072]1001 first bottom electrode in the form of a comb

[0073]1002 second bottom electrode in the form of a comb

[0074]1100 example of a further specific embodiment of a humidity sensoraccording to the present invention having reticular or latticedelectrodes

[0075]1101 p-doped silicon substrate

[0076]1102 p-doped silicon intermediate layer

[0077]1103 reticular lower electrode

[0078]1104 reticular upper electrode

What is claimed is:
 1. A semiconductor component, such as, in particulara humidity sensor (200, 300, 400, 500, 600, 700, 800), which has asemiconductor substrate (101), such as especially of silicon, a firstelectrode (102) and a second electrode (202) and at least one firstlayer (101) that is accessible for a medium acting from the outside onthe semiconductor component, the first layer being arranged at leastpartially between the first and the second electrode, wherein the firstlayer has pores (301), into which the medium has reached at leastpartially.
 2. The semiconductor component as recited in claim 1, whereinthe medium is gaseous or liquid, like especially air having humidity. 3.The semiconductor component as recited in claim 1 or 2, wherein thesemiconductor component is provided with a second porous layer (401)whose porosity, i.e., the relationship of the volume of pores tomaterial, is less than the porosity of the first porous layer (301), thesecond porous layer (401) forming, in particular, the first electrode(202), via which the medium completely or partially reaches the firstporous layer (301).
 4. The semiconductor component as recited in one ofclaims 1 through 3, wherein the first and the second electrodes (102,202) are arranged essentially on the same level with a distance to oneanother, preferably forming an interdigital structure (1000).
 5. Thesemiconductor component as recited in claim 4, wherein the first and/orsecond electrode (102, 202) and/or the first porous layer is/are coveredor protected by a third porous layer (603).
 6. The semiconductorcomponent as recited in one of claims 1 through 5, wherein the firstand/or second electrode is/are formed at least partially by a suitablydoped semiconductor layer (101, 202) and/or by a metallic layer.
 7. Amethod for producing a semiconductor component as recited in one ofclaims 1 through 6, wherein the porous layer (301) is formed by one ormore etching media, the etching medium and/or the etching mediapreferably containing hydrofluoric acid or HF acid, or being made ofhydrofluoric acid.
 8. The method as recited in claim 7, wherein theetching medium or the etching media is/are provided with one or moreadditives, such as additives for reducing bubble formation, forimproving the wetting, and/or for improving the drying, like inparticular an alcohol such as ethanol, the volume concentration of theadditive, like particularly ethanol, preferably being approximately 30%to approximately 90% in the case of ethanol.
 9. The method as recited inclaim 7 or 8, wherein the first and/or second porous layer (301, 401) isformed by applying an electric field between the upper side and thelower side of the semiconductor component and the setting of an electriccurrent which flows through the etching medium or the etching media. 10.The method as recited in one of claims 7 through 9, wherein the measureof the porosity of the first and/or second porous layer (301, 401)and/or the extent of the pores of the first and/or second porous layeris controlled by the current density in the etching medium or in theetching media and/or the concentration of hydrofluoric acid in theetching medium or in the etching media and/or one or more additives tothe etching medium or to the etching media and/or the temperature and/orthe doping and/or the duration of the current flow.